Astronomers reconstruct orbital path of Russian meteor

Astronomers from the Universidad de Antioquia in Colombia
have used footage of the Chelyabinsk meteor to work out what they believe is roughly
its original orbital path around the Sun.

The Chelyabinsk meteor exploded in the sky over the central
Russian city and region on 15 February, creating a shockwave that
shattered windows for kilometres around and injuring more than a
thousand people. Its path was captured by dozens of cameras, many
of which were mounted onto car dashboards -- a common precaution
against liability in Russia, where fraudulent insurance claims are
rampant and road accidents are extremely common.

That footage is the key to working out the meteor's trajectory.
The astronomers were inspired by the work of technologist Stefan
Geens, who writes about Google Earth on his Ogle Earth blog. He had wondered whether he could use meteor
footage and Google Earth to come up with a rough mapping of the
trajectory of the meteor as it entered the atmosphere, using footage from a static webcam overlooking Revolutionary Square
in the centre of Chelyabinsk. Its static position gave it a good
look of the shadows cast by the meteor as it passed overhead, and
knowing the heights of the lampposts in the square and the
distances they stand apart gave Geens the data needed to calculate
the meteor's height using some pretty standard high school maths
(remember SOHCAHTOA?).

After reading this, astronomers Jorge Zuluaga and Ignacio Ferrin
decided to build on it and see if they could work out the orbital
path of the meteor, and thus where it originated from in the Solar
System. They used a second video for their calculation alongside
the one from Revolution Square -- a webcam from the small town of Korkin, which clearly shows the
meteor reaching its peak brightness and exploding almost exactly
overhead -- something they call "an extraordinary coincidence".

This information gave them what they needed to map the
trajectory of the meteor within the atmosphere. They estimate that
it was travelling between 13km/s and 19km/s, brightening up above
Korkin when it was between 32km and 47km high. Using this
information to plot a path through the sky, Zuluaga and Ferrin
simulated 50 different possible orbits for the meteor through the
Solar System based on their ranges of uncertainty. Their results
lead them to state that "the Chelyabinsk meteoroid belonged
unequivocally to the Apollo family of asteroids".

Zuluaga and Ferrin concede that several assumptions underlie
their work, from the inconsistencies in the timestamps on the
different videos to accepting the theory that the hole in the ice
at Lake Cherbakul is the meteor's final impact crater. However, the
main problem was that, unlike the Revolution Square footage, the
dash and handheld cameras were moving around, and weren't near
static objects with easily researched physical dimensions like the
lampposts -- the Korkin video was their least worst option. They
also don't have a firm idea of the impact velocity of the meteor,
which creates uncertainty in their estimates of its velocity when
it entered the atmosphere.

They write: "The largest source of uncertainty in our
reconstruction is the qualitative nature of the observational
evidence in the second vantage point used in the 'triangulation' of
the meteoroid trajectory. Further eﬀorts to clarify this point
should be attempted to reduce the uncertainties in the direction
and velocity of the reconstructed trajectory." Their paper has been
published on the open source journal arXiv for peer
review.

If this trajectory is accurate, it means the meteor came from
the Apollo
group of asteroids that orbit on irregular axes around the Sun.
Their greatest distances from the Sun are larger than 1AU, but
their nearest approaches to the Sun are less than 1AU -- meaning
they cross the orbit of the Earth. Many of the Apollo asteroids are
considered potentially dangerous, though none are known to be
particularly so at the moment. The largest -- Sisyphus -- is 10km
across, and would exterminate most life on Earth if it hit, but its
next closest approach, in 2071, will still be further than 40 times
the Moon's orbit away.

Edited by Olivia Solon

Comments

¡Great article! One of the most enlightening I have read on this topic.